1. Field of the Invention
The present invention relates to multiple channel multiplexer/demultiplexer optical devices. In particular, the present invention relates to a compact demultiplexer device based on wide wavelength division multiplexer bandpass filters.
2. Background Technology
The increasing demand for bandwidth, coupled with the high cost of laying new optical fiber, has created a strong demand to find new and better ways to increase the carrying capacity on existing optical fiber. One such way to increase the capacity is by a technique called wavelength division multiplexing, which is the use of multiple wavelengths to carry multiple signal channels and thereby greatly increase the capacity of installed fiber optic networks.
Wavelength division multiplexing (WDM) technology has become a vital component of optical communication systems. In a WDM optical system, light from several lasers, each having a different central wavelength, is combined into a single beam that is introduced into an optical fiber. Each wavelength is associated with an independent data signal through the optical fiber. At the exit end of the optical fiber, a demultiplexer is used to separate the beam by wavelength into the independent signals. In this way, the data transmission capacity of the optical fiber is increased by a factor equal to the number of single wavelength signals combined into a single fiber.
Demultiplexing (DEMUX) devices are typically designed to selectively direct several channels from a single multiple-channel input beam into separate output channels. Multiplexing (MUX) devices are typically designed to provide a single multiple-channel output beam by combining a plurality of separate input beams of different wavelengths. A multiplexing/demultiplexing (MUX/DEMUX) device operates in either the multiplexing or demultiplexing mode depending on its orientation in application, i.e., depending on the choice of direction of the light beam paths through the device.
Thus, in a WDM system, optical signal channels are: (1) generated by light sources; (2) multiplexed to form an optical signal constructed of the individual optical signal channels; (3) transmitted over a single waveguide such as an optical fiber; and (4) demultiplexed such that each channel wavelength is individually routed to a designated receiver such as an optical detector.
In WDM systems, data carrying capacity is increased by adding optical channels. Conceptually, each wavelength channel in an optical fiber operates at its own data rate. In fact, optical channels can carry signals at different speeds. The use of WDM can push total capacity per fiber to hundreds of gigabytes per second. Generally, more space is required between wavelength channels when operating at 10 gigabytes per second than at 2.5 gigabytes per second, but the total capacities are nonetheless impressive. For example, in the case of 4 wavelength channels at a data rate per channel of 2.5 gigabytes per second, a total data rate of 10 gigabytes per second is provided. With 8 wavelength channels at a data rate per channel of 2.5 gigabytes per second, a total data rate of 20 gigabytes per second is provided. In fact, other wavelength channels can include, for example, 16, 32, 40, or more wavelength channels operating at 2.5 gigabytes per second or 10 gigabytes per second and allow much higher data transfer possibilities. Further, the use of multiple fibers in a single cable can provide even higher transmission rates. The 10 gigabit per second Ethernet standard (GbE) is particularly suited for this technology.
Generally, applications for MUX/DEMUX technology include long haul communications and local area data networks. Both digital and analog systems have been demonstrated for voice, data and video. The scope of applications for WDM devices ranges from spacecraft and aircraft applications to closed circuit and cable television systems. In view of these diverse applications, much effort has been expended toward developing WDM technology.
However, limitations due to crosstalk and channel separation have limited the use of MUX/DEMUX systems in data transfer such as in local area networks (LAN), metropolitan area networks (MAN), and wide area networks (WAN).
One solution to crosstalk and channel separation problems exists in wide wavelength division multiplexing (WWDM), which is an industry-defined term that indicates narrow bands of wavelengths that are spaced relatively far apart. Typically, the wavelength bands are about 10 nanometers (nm) wide and are spaced about 25 nm apart. The wavelength bands in WWDM are centered at about 1310 nm and typically include four channels at 1275 nm, 1300 nm, 1325 nm, and 1350 nm, each within about xc2x15 nm of the designated wavelength.
An advantage of the wide channel spacing in WWDM is that it requires no temperature control over the range of 0xc2x0 C. to 70xc2x0 C. This is because, although laser wavelengths drift by a few nanometers over the range of 0xc2x0 C. to 70xc2x0 C., WWDM""s xcx9c10 nm band width accommodates wavelength variations of xc2x15 nm. Therefore, WWDM is not particularly limited by temperature conditions.
Another advantage of WWDM is that no amplifiers are required because narrow spacing is unnecessary. The entire useful spectrum carried by a fiber can be covered if necessary. For example, as discussed hereinabove, up to 40 wavelength channels or more can be used. Nevertheless, when more than 4 wavelength bands, for example 8 or 16, are multiplexed, the demultiplexing needs become greater and the accompanying risk of excessive beam attenuation heightens.
Similarly, coarse wavelength division multiplexing (CWDM) is another industry-defined term and is an alternative solution to crosstalk and channel spacing problems. In CWDM systems, wavelength bands are about 10 nm wide and are spaced about 20 nm apart. The CWDM bands are centered at about 850 nm and typically include four channels at 800 nm, 820 nm, 840 nm, and 860 nm, each within about xc2x15 nm of the designated wavelength.
In contrast, dense wavelength division multiplexing (DWDM) has much narrower wavelength bands that are spaced closer together. Whereas DWDM is commonly used in telecommunications where the dense channel spacing is ideal, DWDM is normally incompatible with local network data transfer because the narrow channel spacing leads to excessive crosstalk that is unacceptable in data transfer applications. In DWDM systems, channel spacings of less than 1 nm are typically used, with wavelength bands centering around 1550 nm.
In the world of fiber optics, bulk optics are physical objects such as conventional lenses, mirrors and diffraction gratings. However, bulk optics do not have to be large. They can be engineered to be very small, on scale with optical fibers and associated light sources. Even when engineered to be small, however, such systems are still based on the same optical principles as larger bulk optics.
An example of a bulk optics demultiplexer is disclosed in U.S. Pat. No. 4,675,860 to Laude et al. (hereinafter xe2x80x9cLaudexe2x80x9d), which discloses a demultiplexer that utilizes a number of spherical interference filters that are arranged in series along an optical path of a beam of light that is emitted from an optical fiber. Each filter is selected to reflect a particular wavelength to a specific outlet fiber and transmit light of the other wavelengths to the next filter in the series. Each subsequent filter in the series is selected to reflect a different wavelength to a different outlet fiber.
Another example is U.S. Pat. No. 4,993,796 to Kapany et al. (hereinafter xe2x80x9cKapanyxe2x80x9d), which discloses modules for interfacing optical fibers. Kapany discloses the use of concave gratings and dichroic beam splitters to demultiplex multi-channel beams.
U.S. Pat. No. 6,008,920 to Hendrix (hereinafter xe2x80x9cHendrixxe2x80x9d) discloses a multiple channel MUX/DEMUX device that includes optical filters positioned in a zigzag pattern on a wedge shaped optically transparent block. Hendrix uses differing light incidence angles to alter the bandpass of identical filters.
Another example of a demultiplexer is disclosed in European Patent Application Publication No. EP100490782 to Lemoff et al. (hereinafter xe2x80x9cLemoffxe2x80x9d). Lemoff discloses a demultiplexer that includes a unitary optically transparent structure that utilizes focusing/reflecting mirrors to relay a multi-wavelength beam of light among a series of wavelength specific bandpass filters with each filter separating out a specific wavelength component in the multi-wavelength beam. Lemoff disadvantageously uses complex, off-axis aspherical surfaces to initially direct the multi-wavelength beam of light onto the series of wavelength specific bandpass filters and reflecting mirrors.
Currently, conventional WDM multiplexer/demultiplexer devices suffer from many performance deficiencies while consuming a large portion of an optical system""s attenuation loss budget. Such designs are often bulky and are difficult to design and fabricate accurately.
Accordingly, there is a need for improved MUX/DEMUX devices that avoid the drawbacks of conventional devices.
It is an object of the present invention to provide a multiplexer/demultiplexer device in which each optical surface therein can be produced within current standard molding tolerances.
It is another object of the invention to provide a multiplexer/demultiplexer device that is easy to mold and fabricate accurately.
Another object of the invention is to provide a multiplexer/demultiplexer device in which all surfaces are simple geometric forms and are easily accessible for measurement.
It is yet another object of the invention to provide a multiplexer/demultiplexer device that is easy to handle and assemble due to simple component geometries.
Another object of the invention is to provide a multiplexer/demultiplexer device that is easily scalable or modified.
It is a further object of the invention to provide a multiplexer/demultiplexer device that is easy to incorporate into other optical systems.
In order to achieve the forgoing objects and in accordance with the invention as embodied and broadly described herein, multiple channel multiplexing/demultiplexing devices are provided. In general, an optical multiplexer/demultiplexer device according to the invention comprises an input port for receiving a plurality of optical signal channels, and a plurality of output ports. Imaging optical elements such as imaging mirrors are provided for relaying a multi-wavelength beam of optical energy from the input port to at least one of the output ports along an optical axis. At least one wavelength selective reflector is provided in the device for receiving the beam of optical energy reflected from the imaging optical elements and transmitting one or more optical signal channels toward a first output port. The wavelength selective reflector is also configured to transmit one or more optical signal channels toward a second output port, and reflect a beam of optical energy for transmission of one or more optical signal channels at a third output port. At least one reflective surface is provided in the device for reflecting a beam of optical energy received from a first region of the wavelength selective reflector to a second region of the wavelength selective reflector.
Preferably, the operative portions of the reflective surface and one of the imaging mirrors are substantially co-linear. The imaging mirrors are preferably configured to afocally relay the beam of optical energy from the input port to at least one region of the wavelength selective reflector. In addition, at least one of the imaging mirrors preferably has a parabolic surface that comprises the vertex of a parabola, and the device of the invention is preferably configured such that its optical axis is not parallel to an axis of the parabolic surface. Further, the reflective surface can comprise at least one collimating reflector or at least one non-collimating reflector.
One embodiment of the present invention includes an optically transparent optical block seated atop an optically transparent beam-directing member. The optical block includes a plurality of wavelength selective elements, a plurality of reflectors, and at least one imaging optical element. The beam-directing member includes a beam folding mirror and focusing lenses.
More specifically, an optical demultiplexer device is provided that includes a transparent optical block having an upper surface defining a plane, and a lower surface. An imaging optical element is positioned on the upper surface of the optical block and is configured to direct a multi-wavelength beam of optical energy along a predetermined optical path. A plurality of wavelength selective elements are positioned below the upper surface of the optical block and are configured to receive the beam of optical energy. A plurality of reflectors on the upper surface of the optical block are configured in a substantially coplanar linear arrangement with the imaging optical element. The reflectors are positioned opposite from the wavelength selective elements such that each of the reflectors, as part of an imaging relay system, directs the beam of optical energy from one wavelength selective filter to an adjacent wavelength selective filter.
When the device of the invention is used as a demultiplexer, a multi-channel beam is directed into the optical block and relayed in a zigzag pattern onto the wavelength selective elements, which separate selected wavelengths from the beam. The separated wavelengths propagate through the beam-directing member and are focused onto optical receptors.
The foregoing objects and features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.